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B. Bissonnette Laval University, Canada
SAMPLING AND TESTING OF CONCRETE
AS PART OF AN ASSESSMENT
ACI 364.1R (Chapter 6) – Scope
• What are the available methods & tools to supplement the basic
information collected on site for the assessment of a concrete
structure prior to rehabilitation?
• How to sample the structure?
ACI 364.1R (Chapter 6) – Scope
• Practices and methods for evaluating the condition and
properties of materials that govern the behavior of a concrete
structure
field-based nondestructive tests (NDT) and destructive tests
field sampling coupled with laboratory-based tests
Sampling and Testing Requirements
• Need for sampling and field/laboratory testing to be established,
based upon :
review of available engineering documents related to the structure (Chapter 4)
findings of the field investigation (Chapter 5)
establishment of rehabilitation plans
Sampling and Testing Requirements
• Requirements for testing :
inadequate information about the materials in a structure
observed / suspected deterioration or defects (construction or materials)
uncertain load-carrying capacity or serviceability behavior
new requirements on the structure
(ex. increased load demands, enhanced life
safety goals, modified use)
performance of the structure altered by the
planned rehabilitation
Sampling and Testing Requirements
• Many analytical and testing tools available
Selected test method(s) appropriate to yield reliably the required data
Supplemental testing needed as a result of the structure’s exposure to
aggressive environments or natural hazards
• The sampling and testing plan to be developed based on the LDP’s
judgement
Sampling and Testing Requirements
• Selection of suitable test methods and determination of the number
and locations of tests typically depending on :
variation in material properties within the structure
extent of the member or structure over which a specific property is measured
or extrapolated
access to critical locations (ex. connections, lateral load transfer areas)
variations in exposure, loading, and use
availability of sampling/testing equipment and qualified test personnel
Sampling and Testing Requirements
• Selection of test method(s) to diagnose the nature and extent of
distress/deterioration should notably consider :
likely cause(s) or source(s) (ex. corrosion, ASR)
accessibility
structure configuration/geometry
• Special attention required in case of distress caused by prior loading
events (ex. seismic, wind, gravity overload)
Sampling and Testing Requirements
• Sampling and laboratory studies
Sampling location(s) representative of the structure
Primary reinforcing steel prevented from damage
Samples protected during recovery
Sampling and Testing Requirements
• Special considerations for architectural or historic structures*
Testing required / possible
sampling in less visible location
adapted repair procedure for restoring the structure’s appearance
Testing not possible
based upon the date of construction, conservative use of historical values for concrete
compressive strength and yield strength of reinforcing steel (ASCE/SEI 41; ACI 562)
*(ACI 364.2R in development)
Testing and Evaluation
• Evaluation of existing concrete based upon:
existing conditions, strength, and serviceability
properties of the concrete as derived from field tests or laboratory studies on
samples removed from the concrete structure
• Data collection and subsequent evaluation to provide an
understanding of the ability of the structure to sustain the loads and
environmental conditions to which it is subjected
Test Methods
• Test procedures
Hardened concrete
Steel reinforcement
Tests Methods – Hardened concrete
• Mechanical properties
Tests Methods – Hardened concrete
• Mechanical properties
Tests Methods – Hardened concrete
• Mechanical properties
Tests Methods – Hardened concrete
• Durability characteristics & properties
Tests Methods – Hardened concrete
• Durability characteristics & properties
Tests Methods – Hardened concrete
• Condition
Tests Methods – Hardened concrete
• Condition
Tests Methods – Hardened concrete
• Condition
Tests Methods – Hardened concrete
• Condition (…)
Tests Methods – Hardened concrete
• Condition (…)
Tests Methods – Hardened concrete
• Condition (…)
Tests Methods – Hardened concrete
• Condition (…)
Tests Methods – Hardened concrete
• Condition (…)
Tests Methods – Hardened concrete
• Condition (…)
Tests Methods – Hardened concrete
• Condition (…)
Tests Methods – Hardened concrete
• Condition (…)
Tests Methods – Hardened concrete
• Condition (…)
Tests methods – Steel reinforcement
• Reinforcement characteristics and condition
Tests methods – Steel reinforcement
• Reinforcement characteristics and condition
Tests methods – Steel reinforcement
• Reinforcement characteristics and condition
Tests methods – Steel reinforcement
• Reinforcement characteristics and condition
Test Methods
• General considerations
NDT methods* generally preferred to measure material properties where
applicable, to minimize sampling and repair needs
Based on findings of the field investigation, sampling and laboratory studies
used to determine the causes of existing distress or deterioration
(ex. petrographic analysis)
Field load test involving components or the full-scale structure for
supplemental information regarding in-place structural behavior or extent of
distress
feasibility limited by various technical and economical constraints
*(ACI 228.1R, ACI 228.2R)
Sampling Techniques – Concrete
• Concrete samples can be retrieved in the field and tested in the
laboratory to determine strength as well as many other physical and
chemical properties
• Representativeness
appropriate care in all phases
(obtaining, identifying, handling, and storing)
number & location(s) of samples – sampling plan
Sampling Techniques – Concrete
• Development of a sampling plan (ASTM C823)
Scope
statistical information about the properties of concrete in the structure
and / or
characterization of unusual or extreme conditions in specific components
Random distribution desirable in the area of interest of a structure / member
whole area
sub-areas (varying conditions, special structural considerations)
Sampling Techniques – Concrete
• Development of a sampling plan (…)
Sample size for average values of properties (ex. fc, Ec, air % )
ASTM E122, ASTM C42, ACI 214.4R
function of the size of the structure, condition / deficiencies, extent of problems,
available information
Concrete not an isotropic material, with properties that may vary depending on
the location or direction of sampling
special attention to be paid to vertical concrete components or members, such as
columns, walls, and deep beams
Sampling Techniques – Concrete
• Core sampling
Procedures for properly removing concrete samples by core drilling
(ASTM C42)
The number, size, and location of core samples to be selected depending on
the laboratory tests requirements
Recommended use of separate core samples for each different test to avoid
cross-contamination of test results
Sampling Techniques – Concrete
• Core sampling (…)
Average strength from core specimens
only to verify the in-place concrete strength
not to be used directly in calculating the existing load-carrying capacity
appropriate adjustment needed for use in calculations (in-place compressive strength)
3 cores min. at each location in the structure, with the strength value taken as the
average of the 3 cores (ACI 318; ACI 562)
Sampling Techniques – Concrete
• Sampling of concrete with sawed beams (ASTM C42)
Where appropriate, alternative sampling by sawing beam sections
Differences encountered between cores and sawed beam samples to assess
the actual in-place concrete strength (ACI 214.4R; ASCE/SEI 11)
• Random sampling of broken concrete
Inappropriate for evaluating mechanical properties of concrete
Acceptable for assessing chemical / physical deterioration using laboratory
analyses (note: cause of the fracture to be evaluated)
Sampling Techniques – Steel reinforcement
• Samples of reinforcement tested for determination of physical or
chemical properties of the reinforcing steel
• Sampling: characteristics, selection, and preparation (ASTM A370)
(testlabs.ca)
Sampling Techniques – Steel reinforcement
• General considerations – conventional reinforcement
Specimens removed at locations of minimum stress
Only one specimen removed from the same cross section of a member
Specimen locations apart at least the development length (ld)
For structural members investigated
span < 25 ft or loaded area < 625 ft2: at least one specimen from the main
longitudinal reinforcement (not stirrups or ties)
(ACI 437R)
longer spans / larger areas: more specimens from locations well distributed to
detect potential differences in steel grade
Sampling Techniques – Steel reinforcement
• General considerations – conventional reinforcement (…)
Information from grade / mill marks on rebars for guiding sample collection
Newer reinforcing steel: typically exhibits low variability and less sampling needed
Older structures with smooth/square/iron-based reinforcement: potentially more
extensive
Minimum gauge length for mechanical properties in accordance with ASTM
A370
Shorter samples (> 4 in) useful to yield information on physical and chemical
properties
Sampling Techniques – Steel reinforcement
• Sampling of prestressed reinforcement for laboratory
Testing with care using appropriate safety procedures
Unbonded tendons with accessible anchorages
visual examination
lift-off tests to measure the prestress force
sampling generally not recommended unless structural capacity is threatened
Test Reporting
• Scope of sampling and testing completed
• Lab certification information
• Date of testing and personnel involved
• Equipment used and accuracy/calibration information
• Alignment of sampling/test performed with plan document
• Test execution observations and results
• Data recovered, sorted by specific tests completed and data type
• Assessment of test results and extrapolation of such relative to the concrete structure as a whole
• Recommendations for additional testing or other action
Recommended